Method of producing rimmed steel



United States Patent original patent but forms no part of this reissuespecification; matter printed in italics indicates the additions made byreissue.

This invention relates in general to a method of manufacturing rimmingsteels. In particular, it relates to a method of manufacturing rimmingsteels of the capped variety in which reactive agents are added to themolten steel in the ladle to substantially reduce the size and effectthe random distribution of non-metallic inclusions in products producedtherefrom.

Modern rimming steel ingots must be produced in such manner as to havegood inherent surface quality and good inherent internal qualities whichwill result in substantially trouble-free fabrication into useful andsatisfactory products.

The aforementioned steels are subjected to drastic reductions in beingprocessed from the ingot or semifinished form into finished steelproducts; as for example, finished sheet, tin and strip mill products.They may be subjected to severe deformation in subsequent drawing and/orforming operations and also to impregnation with hydrogen gas duringpickling and vitreous enameling operations. For the above reasons, it isnecessary for the ingot to have a good primary surface quality, i.e.,have a skin of sufficient thickness and also be substantially free ofnon-metallic inclusions of appreciable length and breadth.

In order for the ingot to rim properly and consequently possess therequired type of ingot skin, the rimming steel must have a suflicientamount of available oxygen dissolved in the molten metal when the ingotis poured. The said available oxygen is needed to sustain the optimumdegree of carbon-oxygen rimming action to produce a skin or rim on thesurfaces of the ingot. The said carbon-oxygen rimming action is of sucha nature that only small or Vernier additions to the mold of beneficialdeoxidizing or other appropriate substances are required to control it.

The ingot consisting of a skin of substantially pure iron and a core,said core being substantially ferritic in nature and containing varyingamounts of carbon, manganese, phosphorus, sulfur and silicon and smallamounts of other residual elements normally present in such steels,produced as above, must also have internal quality sufficiently good toproduce a good secondary surface, i.e., the new surface which resultswhen the primary rimmed skin is inadequate in thickness or is locallyremoved as in scaling or scarfing or when new surface area is producedconcurrent with reduction of section in processing. In order toaccomplish the desired end result, the nonmetallic inclusions,unavoidably present in all rimming steels and particularly in rimmedsteels which are capped, must be small and must be well-dispersedthroughout the ingot rather than segregated at the interface between theskin and core or in the ingot skin itself.

The non-metallic inclusions normally present in these steels areordinarily of the stringer variety and are largely oxides, sulfides andsilicates. These inclusions can be large, hard, and brittle, and if theyform near the surface of the ingot will break through the surface ofsteel during subsequent hot or cold reducing operations forming skinlaminations" or localized surface imperfections resulting in anunsatisfactory product. Due to the deformations involved in subsequentdrawing or other cold forming operations the said inclusions can alsoresult in localized failures during deformation or break through thesurface of the steel resulting in unusable or inferior products. Theaforementioned inclusions may also become focal points into whichnascent hydrogen can penetrate during acid pickling and vitreousenameling operations. Molecular hydrogen will not diffuse through coldsolidified metal. Therefore, the accumulation of the molecular hydrogenor the increase in its volume and its attendant greater pressure,especially when the article is heated rapidly, becomes great enough toform blisters in the sheet rendering the article unsatisfactory for use.

It is the primary object of this invention to produce a rimming typesteel which has smaller and more widely dispersed non-metallicinclusions than heretofore obtainable.

It is another object of this invention to produce an ingot of rimmingtype steel having good inherent primary surface quality and superiorinternal quality by the addition of an oxidizing agent and a deoxidizingagent to the molten steel while it is in the ladle.

It is another object of this invention to produce an ingot of rimmingtype steel which can be processed into useful and salable products witha minimum amount of various internal and surface imperfectionsattributable to dirty steel.

It is still another object of this invention to produce an ingot ofrimming and/or capped type steel which may be processed into doublereduced tinplate with a minimum amount of rejections due to surfaceblemishes or internal imperfections resulting from non-metallicinclusions in the steel.

It is another object of this invention to produce an ingot of rimmingtype steel which can be formed into useful products by rolling, drawingand pickling and enameling operations with a minimum amount ofrejections.

It is another object of this invention to produce a rimming steel whichwhen processed into useful articles by welding, will produce a weldwhich is more reliably stronger and sounder than heretofore producedfrom such steels.

I have found that by adding an oxidizing agent to a rimming steel duringthe tapping of the molten metal into the ladle the amount of dissolvedoxygen in the steel is increased. By adding an amount of a suitabledeoxidizing agent in the ladle to react with the excess oxygen, theformation of large globules and stringer type non-metallic inclusions isinhibited. The steels treated by my process are characterized by thepresence of smaller, better dispersed non-metallic inclusions and by adiminution in severity of the stringer-type inclusions usuallyassociated with rimming steels. By "smalr inclusions is meant thoseinclusions present in the steels treated according to the presentinvention, substantially all of 'which are smaller than those normallyobserved in rimmed steels. As a result, it is possible to produce aningot which may be processed into finished steel products with anegligible amount of rejections due to skin laminations or surfaceblemishes or other injurious imperfections developing in processingoperations and subsequent forming or drawing operations; including theformation of blisters during pickling and vitreous enameling operationsand to the incidence of Weak spots in welds associated with inclusionsof significant size.

My preferred method of manufacturing a rimming type steel comprisesadding iron oxide (for example, mill scale) in the ladle to the moltenmetal as it is being tapped from the furnace. The said iron oxide isadded in a dry finely divided state. Beneficial results have beenobtained when using amounts of the said oxidizing agent ranging fromabout 0.05 pound up to about 4.0 pounds per ton of molten metal. Inconjunction with the added iron oxide, aluiminum is also added to themolten metal in the ladle. It has been found that the maximum amount ofaluminum to be added at this time is the amount of aluminum that willcombine with substantially all of the added oxygen effectivelyintroduced into the steel. This achieves the beneficial results of theinvention, i.e. forming small non-metallic inclusions rather than largeglobular and stringer types often heretofore obtained. These beneficialresults, however, can also be achieved by adding aluminum in amountssomewhat less than sufficient to react with substantially all of theadded oxygen effectively introduced in the steel. For example, additionsof up to 2.0 pounds of aluminum per ton of steel can be added to themolten metal in the ladle with beneficial results.

Thereafter standard practices for making rimmed or capped steel arefollowed. Further aluminum additions may be made in the ladle or themold to control rimming action, but not in amounts sufficient to resultin a killed steel.

The molten metal is then teemed into [ingot] molds and the rimmingaction controlled by appropriate additions made to the mold. Although itis not essential to the present invention, aluminum may be added in themold to control the rimming action. This latter addition has been foundto aid in the achievement of the final result.

The above process results in an ingot having small and finely dividedwell-dispersed non-metallic inclusions well under the skin of the ingotinstead of large globules and stringer type non-metallic inclusionsnormally found in steels of this type. Ingots possessing this type ofnonmetallic inclusions have been rolled, welded, deep-drawn and pickledand vitreous enameled with a minimum amount of difficulty and rejectionsdue to skin laminations, surface blemishes and blisters, or otherdifficulties associated with larger size non-metallic inclusions, andparticularly when at or near the surface.

A specific example of the present invention involved the manufacture ofan 0.08% maximum carbon, .25/.40% manganese mechanically capped rimmigsteel. The heat was melted in the manner usual for rimming steels andtapped. During tapping, about 1.2 pounds per ton of very finely divided,dry, mill scale (i.e. iron oxide) was added to the ladle. This was doneafter a cushion of about 18 inches to 24 inches of steel had been tappedinto the ladle. Immediately after the addition of the mill scale, about0.15 pound per ton of shot aluminum was added to the molten metal in theladle. The shot luminum combined with a portion of the oxygen, i.e.,oxygen which is normally present in the steel plus the additional oxygenmade available by the mill scale addition, dissolved in the molten bath.The resultant reaction formed small non-metallic inclusions, complexFeO:Al,O and A1 which were widely dispersed throughout the bath. Theamount of aluminum added was sufficient to combine with substantiallyall of the elfectively introduced added oxygen, but there remained inthe steel an amount of oxygen equal to that normally found in the steelplus a portion of the excess amount which had been deliberately added.After the heat was tapped 0.19 pound of aluminum per ton of steel wasadded to the ladle to react with a portion of the remaining dissolvedoxygen. In order to bring the heat to the required manganese content,9.9 pounds of ferromanganese per ton of steel was added to the ladle.The heat was teemed into ingot molds, with about ounces of aluminumbeing added to each mold to control the rimming action. The sheet steelproduced from this heat was used for various applications, a portionbeing processed into double reduced tinplate, a portion was applied onorders for hot rolled sheet subsequently processed into auto wheel rims,and a portion was applied on orders for cold rolled sheets.

In the processes of making prior art rimming steels of the cappedvariety, the rimming action begins as in a regular rimmed steel but isterminated after a short rimming period by sealing the mold with a steelor cast-iron cap or by chemical means. The product of this standardprocedure is an ingot having a thin rimmed skin and large non-metallicglobular and stringer type inclusions trapped in the ingot by thecapping procedure. As a result, these steels usually appear dirtier thanregular rimmed steels.

The steels treated in accordance with the present invention are cappedin the usual manner. But because of the inhibition of the formation oflarger non-metallic inclusions, the above steels appear cleaner whenviewed at magnifications (normally used in metallographic study) than dothe capped steels made in the usual manner. The inclusions formed in myprocess are finer and more widely dispersed, and fewer of them arediscernible at such magnification.

I have described the preferred method of the present invention above,but the order of the ladle additions cited may be altered or evenreversed. For example, aluminum may be added to the molten metal in theladle either prior to, during, or after the addition of the oxidizingagent employed.

Iclaim:

1. A method of manufacturing a rimming type steel comprising:

(a) melting a heat of steel and tapping the molten metal into a ladle,

(b) adding to the molten metal in the ladle a solid oxidizing agent,

(c) adding to the molten metal in the ladle aluminum in an amount nomore than suflicient to combine with substantially all of the oxygen insaid oxidizing agent,

(d) and teeming the treated metal into [ingot] molds.

2. A method as claimed in claim 1 with the said oxidizing agent of step(b) being mill scale.

3. A method as claimed in claim 1, said oxidizing agent of step (b)being mill scale added in the range of about 0.05 pound up to about 4.0pounds per ton and the aluminum of step (c) being added in an amount upto about 2.0 pounds per ton.

4. A method as claimed in claim 1, said oxidizing agent of step (b)being mill scale added in the range of 1.0 pound up to about 2.0 poundsper ton of steel and the aluminum of step (0) being added in the rangeof 0.05 pound up to about 0.5 pound per ton of steel.

5. A method of manufacturing a rimming type steel comprising:

(a) melting a heat of steel and tapping the molten metal into a ladle,

(b) adding to the molten metal in the ladle a solid oxidizing agent,

(c) adding to the molten metal in the ladle aluminum in an amount nomore than sufiicient to combine with substantially all of the oxygen insaid oxidizing agent,

(d) teeming the treated metal into ingot molds,

(e) and capping the ingots.

6. A method as claimed in claim 5 with the said oxidizing agent of step(b) being mill scale.

7. A method as claimed in claim 5, said oxidizing agent of step (b)being mill scale added in the range of from about 0.05 pound up to about4.0 pounds and the aluminum of step (c) being added in an amount up toabout 2.0 pounds per ton.

8. A method as claimed in claim 5, said oxidizing agent of step (b)being mill scale added in the range 5 of from about 1.0 pound up toabout 2.0 pounds per ton of steel and the aluminum of step (c) beingadded in the range of from 0.05 pound up to about 0.5 pound per ton ofsteel.

References Cited The following references, cited by the Examiner, are

of record in the patented file of this patent or the original patent.

UNITED 6 STATES PATENTS Smith 75-56 Reeder 75-53 Jordan 75-58 Boucek75-53 Rossborough 75-53 BENJAMIN HENKIN, Primary Examiner.

